Clutch spring



Sept. 22, 1936. c, DREXLER CLUTCH SPRING Filed Dec. 3, 1932 Patented se ezz, 1936 g I 2,055,068 I UNITED STATES PATENT OFFICE cw'rcn seams Charles Drexler, Indianapolis, Ind., assignor, by

mesne assignmentato William C. Starkey, Raymond S. Pruitt, and Walter H. Beal, trustees Application December 3, 1932, Serial No. 645,527 3 Claims. (01. 192-107) This invention relates to improvements in turning but it has been found that even with the clutch springs and it consists of the matters herebest grinding equipment available, it is very nearinafter described and more particularly pointed ly impossible. to grind a true cylindrical surface out in the appended claims. on a spring having the straight continuous grooves 5 The type of spring with which the present inbeforementioned. I have discovered that the 5 vention is more particularly concerned is helical reason for this inability to produce a true cylindriand is adapted for use in connection with a pair cal surface on such a grooved spring is that of coacting, rotating, clutch members which upon the grinding wheel tends to drop into said grooves. a relative rotation in one direction so act upon This sets up a chatter or vibration in the spring the spring as to cause it to change its diameter so thatthe finishedspring has a surface contour and clutch the members together for conjoint resembling a; many sided polygon with rounded rotation. corners and therefore obviously not best suited To make springs of this type more sensitive in for clutching purposes. their action, certain expedientshave been tried. An object of the invention is to provide an im- In one instance, longitudinal grooves have been proved grooved spring, having a more nearly true 15 provided in the coils in one end of the spring, cylindrical gripping surface. with the grooves being the deepest at the extrem-' Another object of; the inventionis to provide ity 'of said end. In this manner, the convolua spring, of the kind above mentioned, wherein tion at said extremity,wasthe most flexible and the grooves in certain coils f a r up f oil the succeeding coils or convolutions decreased in are circumierentially offset with respect to those flexibility toward the other end of the grooves in other coils of said groupso that the length of which was located at a point about midway beany particular groove presented to the grinding tween the'ends of the spring. wheel in the grinding operation is so short that These grooves were formed in any suitable the wheel cannot enter or drop into the same, and

manner, as for example, with the aid of an abraso that no vibration is set up in the spring as 25 sive wheel. Such springs were heat treated for will interfere with its being readily ground to a tempering and hardening and finally turned or highly accurate cylindrical surface. ground to make them as cylindrical as possible The above mentioned objects of the invention, and to provide the gripping surface therefor. as well as others, together with the many ad- Usually these grooves are provided in the external vantages thereof, will more fully appear as I pro- 30 surface of the spring because of the ease with ceedwith my specification. which they could be there formed and in other Inthe drawing: instances the interior surface of the spring Fig. 1 is a view'in side elevation of a spring after formed the gripping surfaces. Such clutch it has been wound to form what may be called a springs were differentiated by the terms outside' spring blank ready for other operations there- 35 grip" and inside grip" respectively. In either on; instance, it was of course desired that the grip- Fig. ,2 is a view in side elevation of the spring ping surface be as truly cylindrical as possible. blank and illustrates one manner of providing The various operations on the spring such as certain arcuately spaced, gradient grooves in a 40 winding, bending the same to form the anchoring group of t coils atone end of the spring, as 40 we 0 time a the grooving which usually 1 by grinding and also shows the initial disposition ceded the grinding Operations set up Strains in of said grooves as continuous ones in said spring the spring. These strains are quite apt to maniblank; fest themselves in m ways and produce 9 Fig. 3 is a view in side elevation of the spring 5 tortions and crystalhzations which at times cause after having been longitudinally grooved as the spring to break in use. ,As a clutch spring in a clutch of the kind so n 3 m side elevatio and using the same, depends on friction for its hold- .vlew pa y m b h ing power, its gripping surface, whether on the partly m sectmn of tubular M w c 1s the spring blank shown-in inside or outside of the spring, must be as cylinforced or pressed into 50 drical as possible and as the spring is inher- 3 from grooved end to r e thediam- .enfly flexible, t is apparent t t t is quite geter of the spring and cause staggering or circumficult to so turn or grind said surface accurately ferential ofisetting of parts of the grooves in to the desired diameter. certain of the coils or convolutions and at the i Grinding such surfaces is much superior to same time provide a support for the spring blank 55 when subjected to a normalizing treatment to impart a set to said blank;

Fig. 5 is a view partly in side elevation and partly in section of the thus far completed spring after the arbor shown in Fig. 4 has been pressed thereinto to expand the spring and cause the staggering or circumferential offsetting of the grooves; and

Fig. 6 is a view in end elevation of the spring shown in Fig. 5 after the arbor of Fig. 4 has been removed therefrom so that the spring is ready for its grinding operation. In general, in accordance with the invention, a suitable length of spring stock is wound in accordance with standard spring practice into spring form to provide a spring blank. When the finished spring is to 2 inches, the spring stock used therefor is of such a cross section as to provide an inside diameter of approximately 1.955". These dimensions of course, vary in proportion in springs of diiferent sizes. If the spring is to have a holding toe or tang the samemay be provided after such a winding.

Such a completed spring or blank is then oper ated upon to provide arcuately spaced grooves in preferably the external surface of a group of its coils and which group constitutes the coils at that end opposite the toe. Said grooves are deepest at that end opening at the extremity of said spring end, and gradually die out at the other end into said external surface at a point about midway between said ends of the blank.

A tubular arbor having an outside diameter about .060" larger than the inside diameter of the thus far completed spring or blank is pressed into the same from its grooved end. This radially expands the blank and enlarges its diameter and causes the convolution or coils thereof to slip around so that the grooves in certain coils of the group are circumferentially offset and staggered with respect to the grooves in other of said coils in said group.

With the arbor thus pressed into the thus far completed blank said blank and arbor as a unit, are placed in a normalizing furnace and heated to and held at the desired temperature for a predetermined time period and thereafter quenched.

The arbor is next pressed out of the spring which retains most of its set or enlargement, the grooves remaining in substantially their offset or staggered arrangement in said coils. Thereafter the spring is finished oil. as by grinding to that diameter to fit the surface with which it is to thereafter grip in clutching relation.

The above generalization applies to springs made of steel wire or stock that has been hardened and tempered before winding as this is the most economical practice, but should the spring be made from unhardened and untempered stock. the hardening and tempering operations may be carried out after the arbor has been pressed into the blank and may follow the grooving operation.

Referring now in detail to that embodiment of the invention, illustrated in the drawing: I first take a suitable length of spring stock and following usual spring practice, wind the same into the spring form or blank I shown in Fig. '1. Preferably such stock is first hardened and tempered before such winding. If the spring is to have an anchoring toe or tang 2, the same may at this time be conveniently formed by bending the end of one of theendmostcoils or convolutions so as to extend axially as best shown in Fig. 1. v

have an outside diameter of In a finished spring of a 2 size, the formed blank therefore will have an inside diameter of approximately 1.955", these dimensions of course, varying in proportion in springs of different sizes.

The thus formed blank is then slipped upon the arbor 3 of a grinding machine and which arbor is of approximately the same diameter as the inside of said spring blank. The grinding machine includes a relatively narrow grinding wheel 4 which forms longitudinally extending, arcuately spaced grooves 5 in one end of the springs. Preferably said grooves which are continuous in length, are gradient and begin a suitable distance from the toe end and are deepest at the other end where they open through the extremity of the other end of the spring. The grooved spring blank is then removed from the arbor 3 ready for the next operation.

I then provide a. hollow or tubular arbor 6 as best shown in Fig. 4. This arbor, which is suitably heat treated to hold its temper under high temperatures, has an outside diameter slightly greater than the grooved spring blank. The ends of said arbor are beveled as at I to permit the easy entrance of the arbor into the spring. Such an arbor which is of a length approximating that of the spring is then pressed into the grooved blank from its grooved end.

As said arbor is of an outside diameter greater than the inside diameter of the said blank, its insertion or pressing into the blank enlarges the diameter of the blank and causes a relative circumferential movement or slipping between the adjacent coils or convolutions of the blank. In this movement or slipping of the coils parts of the grooves in alternate coils are circumferentially ofiset about midway between the parts of the grooves in the intermediate coils. Of course, to obtain this result the number of grooves must be adequate and the diameter of said tubular arbor properly proportioned therefor.

The arbor with the toed and grooved spring blank thus mounted thereon in its expanded condition, is then placed as a unit in a normalizing furnace and subjected to a relatively high temperature for a given length of time and is then quenched. For springs of the 2 diameter before mentioned, temperatures from 600 to 800 F. provide the desired results in about an hour. As the arbor is tubular it will heat up quickly.

Said arbor is now pressed out of the spring blank which will retain most of its enlargement resulting from pressing the arbor thereinto and the groove parts will remain staggered or circumferentially offset in the various coils.

The spring is next operated upon externally to fit it with respect to that surface of a clutch with which it is intended to grip. This operation may be either a turning or a grinding one and preferably the latter because of the economy involved and which grinding may be carried out on a centerless grinder.

Heretofore when the grooves were continuous or uninterrupted in length, during the grinding operation, the grinding wheel tended to enter said grooves. This set up a chatter or vibration in the spring so that the ground and finished spring had a contour resembling a many sided polygon with rounded corners and which contour was not best suited for clutching purposes. The spring being inherently flexible, the difliculty in grinding the same is readily apparent. With the spring somade that parts of the grooves in certain of the coils in a group thereof are oflset'or staggered with respect to groove parts in other coils of said group, the length of said groove parts is so short thatthere is no tendency for grinding wheel to enter or drop into said groove parts. Thus the spring does not chatter or vibrate and therefore it can be ground to a highly accurate cylindrical surface.

The various operations upon the spring, such as winding up the spring stock into spring blank form, the bending of the end of one convolution to provide the toe or tang, and the grooving set up certain stresses and strains in the metal of the spring. These stresses and strains are such that'tend to distort and crystallize the spring when in, use, but the normalizing operationbefore mentioned, relieves these strains and stresses and toughens the spring so that distortion and breakage are avoided.

Themethod of making the spring has been de scribed as with the spring blank being wound from tempered stock but this is not absolutely necessary. The spring stock may be formed from "softi untempered stock and then grooved as be- 1 fore described. Thereafter the arbor may be pressed thereinto and the hardening and tempering carried out while so mounted on the'arbor. Preferably the arbor is removed from the spring blank before grinding.

A clutch spring made as described has a very accurate, cylindrical clutching surface whichcoacts with the surface in the clutch member to be gripped and provides that frictional engagement therewith necessary for the holding power for which it was designed. Such a spring is more uniform in character and therefore hasa greater period of usefulness in a clutch.

While in describing the invention, I have referred in. detail to the various steps in the method of making the spring, as well as to the sequence of such steps and the structure of the finished spring, the same is to be consideredmerely as illustrative so that I do not wish to be limited thereto except as: may be specifically set forth in the appended claims.

I claim as my invention:

1. As a new article of manufacture, a helical clutch spring adapted when axially twisted to change its diameter from a predetermined one to a clutching one wherein it serves to clutch together two coacting clutch members for conjoint rotation, and having axially extending, longitudinally aligned grooves in a group of coils thereof and also having axially extending, longitudinally aligned grooves in another group of. coils arranged so that when the spring is of said predetermined diameter they are circumferentially off-set with respect to the grooves in the coils of said one group.

2. As a new article of manufacture, a helical clutch spring adapted when axially twisted to change its diameter from a predetermined one to a. clutching one wherein it serves to clutch together two coacting clutch members for conjoint rotation, and having axially extending, longitudinally aligned grooves in every other coil at one end thereof and also having axially extending, longitudinally aligned grooves in the alternate coils at said one end thereof arranged so that when the spring is of said predetermined diameter they are circumferentially off-set with respect to the first mentioned grooves.

3. As a new article of manufacture, a helical clutch spring adapted when axially twisted to increase its diameter from a predetermined one to a clutching one wherein it serves to clutch together two coacting clutch members for conjoint rotation, and having external, axially extending, longitudinally aligned, equidistantly spaced grooves in every other coil at one end thereof, and also having external, axially extending, longitudinally aligned, equidistantly spaced grooves in the alternate 'coils at, said one end thereof arranged so that when the spring is of said predetermined diameter they are off-set and centrally positioned with respect to the first mentioned grooves.

- CHARLES DREXLER. 

